Plant Tissue Testing Interpretation (7/7/11)

Plant tissue tests should be taken two by two. Each ‘bad’ sample should have a ‘good’ area mate. A soil test is also a very good chaperone.  Nutrient content is different by variety and the ‘critical level’ test values are so archaic that I use relative values more than the actual test number.

Most people looking at a plant tissue test do not realize that the critical levels for most nutrients were developed during the 1950’s and 1960’s. My master’s degree project in corn looked at N/P/K content of grain during the years of 1975-76. General levels of N were higher compared to grain today. A number of tests on wheat have been reported to be “deficient” in micronutrients such as boron, zinc and copper. However, I do not think that these ‘critical levels’ defined by the lab interpretation are correct. Again, if a grower compares ‘bad’ to ‘good’, he usually finds that ‘deficient’ micronutrient levels are present in ‘bad’ and ‘good’, which means to me that the micronutrients are not ‘deficient’ at all.

I would caution against any micronutrient application directed solely by a plant tissue test for a micronutrient not normally applied to the crop and certainly not directed by a solitary test without a ‘good’ mate pair for comparison.

Dave Franzen  - NDSU Extension Soil Specialist

 david.franzen@ndsu.edu